The present invention relates to a device consisting of an oleodynamic distribution system of the rotating type.
More particularly, the present invention relates to an oleodynamic distribution system of the rotating type that can be fit into applications of the oleodynamic type such as for example power steering systems of one or more steering rear axles of vehicles.
The present invention finds a particularly suitable application in the fields of mechanical industry, agriculture and transportation.
Italian patent application N. EO92A327 discloses a power steering system for power steering systems of the rear steering axle of a vehicle, particularly of a heavy vehicle.
It is the aim of the invention described in the present application that of connecting the front steering system of the vehicle comprising a hydraulic power steering system with the rear steering axle of the vehicle itself, so that a steering manoeuvre carried out by the driver operating on the steering wheel causes a simultaneous and coordinated rotation of the front wheels and of the rear steering axle of the vehicle.
In order to accomplish the above aim, according to present invention, the action is exerted by a double effect actuator whose body is connected to an arm that is rigidly coupled to the pivot that allows the rotation of the wheel about a vertical axis, said arm being connected to a corresponding arm for the rotation of the other wheel of the rear axle by a suitable connecting bar.
The piston encased inside the actuator is fixed to the axle of the vehicle by the end of the stem, and it cuts the inside volume of the body into two distinct chambers, each of which being suitable for being filled with pressurised oil with an oleodynamic control and in so doing for causing the displacement of the body of the actuator which in turn causes the simultaneous rotation of the two wheels of the axle.
According to a form of embodiment of the present invention, the lever of the hydraulic power steering system of the vehicle is connected to the actuator by a flexible cable of the Bowden control type, one end of which is directly connected to the slide valve of the two way and three position axial translation movement distribution system that is fixed onto the body of the actuator; in such a configuration, the steering manoeuvre carried out by the driver on the steering wheel is transmitted to the slide valve of the distribution unit by the hydraulic power steering system and by the Bowden control cable, as a consequence of which the slide valve of the distribution system is displaced, connecting the hydraulic power circuits which are suitable for forwarding the pressurised oil to either of the chambers in the double effect actuator in order to operate the steering of the rear axle.
A system that is similar to that described above was disclosed by European patent application n. EP-A-710601.
In the above case the steering system, that also exploits a double effect actuator, can be controlled by a two way, three position axial distributor, and it is applied to the steering of one or more axles in a vehicle semitrailer or trailer.
In both cases the power chassis front wheel steering angle or, for a semitrailer, the fifth wheel rotation angle, is transferred to said axial distributor by suitable means, for example a Bowden control cable driven by a double effect second actuator.
European patent application number EP-A-786394 discloses an improvement of the system object of the above cited European patent application n. EP-A-710601.
The improvement is therein given by the presence of a double effect actuator which connects between the rotation pivot of the wheel to drive and the axial distribution system; therefore, consequently, the axial distribution system is in this case connected to two double effect actuators, both of which with their bodies rigidly coupled with the rotation pivot of a single wheel.
The distribution of the single pressures among the several hydraulic power circuits therein makes it possible to obtain the steering precision.
Document U.S. Pat. No. 4,955,630 which was filed prior to the above cited European patent applications, discloses a steering system for one couple of semitrailer axles.
Even in this case a sensor for the detection of the angular position of the fifth wheel is provided, with respect to the semitrailer, as well as a Bowden control cable in order to transfer the rotation to an axial type distribution unit.
A double effect actuator is driven by said distribution unit in order to simultaneously set the wheels of one or more axles in rotating motion.
Other steering systems for third axles of power chassis, or for single or multiple axles of semitrailers and trailers provided with at least a two way and three position axial distribution unit are respectively disclosed in European patent n. EP-B1-386370, in U.S. Pat. No. (A) 5,244,226, in international PCT patent N. WO-A-8907065 and in Italian patent N. IT-A-1263504.
The above cited steering systems which are provided with a distribution system of the axial type wherein there is found to be present a slide valve that can be translated along a straight line have some remarkable drawbacks and disadvantages that limit their use, complicate their general mechanics of the system and do not make it possible to envisage the possibility to find additional safety systems provided in case of faults or failures.
In particular and with reference to the systems respectively described by Italian patent application N. BO92A327 and by European patent applications N. EP-A-710601 and N. EP-A-786394, these are provided with an actuating cylinder whose stem is fixed, whereas the movable member is made up by the body of the cylinder itself.
This solution which is made inevitable by the hydraulic control of the steering system of the axle to be rotated requires the employment of a purposefully built actuating cylinder. This results to be expensive, and it does not allow the use of the cylinders normally found in the trade.
Furthermore, in this case the two way and three position distribution system must necessarily be rigidly coupled with the body of the cylinder, that is to the mobile part; for this reason, the Bowden control cable that rigidly connects the hydraulic power steering system lever to the slide valve of the distribution unit must be provided with an expansion member located between the hydraulic power steering system lever and an end of said cable, in order to allow the hydraulic power steering system lever to move even when the body of the cylinder and the wheels of the rear axle are blocked in their most unfavourable position.
The above solution further complicates the general mechanics of the system, raising its costs and introducing possible causes for failures and faults.
Furthermore, conventional systems are not provided with any type of safety device that operates in case of faults or breakdowns of the Bowden control cable or of other connection members during the steering; when such a possibility occurs, there is found to occur an immediate dangerous circumstance because the axle cannot be controlled by the hydraulic power steering system of the power chassis and its wheels tend to remain steered towards where they were directed at the moment the breakdown occurred.
To complete the present section, attention is drawn to the fact that there are found to be known in the art two way and three position distribution systems of the rotating type; said rotating distribution systems are used for hydraulic power steering systems of both light and heavy vehicles, and they fulfil their only function to turn the lights of the distribution system on and off in order to direct the pressurised oil to either of the chambers within a power cylinder.
For this function that they must fulfil, said rotating distribution systems have an extremely limited rotation angle, namely in the 5xc2x0-6xc2x0 range, and the movable members are provided with suitable stops that limit the rotation to the above indicated values.
Document DE-A-2655379 discloses a hydrostatic system in which the main shaft (1) is connected to the steering wheel (115) that causes an angular rotation of about 6 to 8 turns.
The hydraulic distribution group is formed by three components, i.e.:
a fixed external body (4) comprising the joints to the hydraulic pipes;
an intermediate ring (6) for the hydraulic distribution, which is, on on side, mechanically connected to and controlled by said shaft (1), while on the other side it is connected to a distribution core (7) through the action carried out by a spring-loaded ball (9), that is incorporated in said intermediate ring, on a flaring of said distribution core. After reaching a minimal rotation torque, which is necessary for operating a motor-pump (12), which determines a radial displacement of ball 9, and after a rotation of about 4xc2x0-6xc2x0, which is necessary for operating the hydraulic distribution, the core is mechanically driven by the intermediate ring through a suitable pin (46);
a distribution core (7) which, on one side is mechanically connected to said intermediate ring and, on the other side, is connected to an internal gear of said motor-pump 12.
It can be noted that said motor-pump group 12 is used as element for controlling the oil flow, and it is indispensable for controlling the whole hydraulic distribution. Without said motor-pump group 12 the rotative distributor (4-6-7-8-9-46) may not work, and the oil flow would permanently stay in a by-pass condition.
A similar distribution core, allowing a rotation of only 4xc2x0-6xc2x0 is disclosed in document U.S. Pat. No. 4,705,129.
Document GB-A-2306927 discloses an hydraulic-electronic power steering system in which (see FIG. 1 of said document):
an electric motor-actuator-group (11) is operated by a regulating circuit (16) which, on its turn, is controlled by the signals coming from position 15 of steering wheel 14 and from position 17 of servomotor 9. The angular rotation is limited to a minimal value that is necessary for controlling the hydraulic distribution and for avoiding the yield of a torsion bar (10);
a rotative hydraulic distribution group comprising three coaxial components, i.e.: (a) an external fixed body (1) including the joints to the hydraulic pipes, and that, on one side, is mechanically connected to an intermediate ring (2xe2x80x3) and to said torsion bar (10) and, on the other side, is connected to the stator of the electric actuator-motor (10); (b) an intermediate ring (2xe2x80x3) for carrying out the hydraulic distribution, which is locked on said body (1) and which is mechanically connected to a distribution core (2xe2x80x2) by means of said torsion bar (10); and (c) said distribution core (2xe2x80x2) which is connected to the rotor of the electric actuator-motor (10). The rotation torque created by the eletric actuator-motor (10) determines the relative rotation between said core (2xe2x80x2) and the intermediate ring (2xe2x80x3) for an angle comprised between 1xc2x0 and 6xc2x0, corresponding to the angle which is strictly necessary to control the hydraulic distribution. Furthermore, a rotation exceeding 6xc2x0 may not be tolerated by the torsion bar.
Documents EP-386370, EP-A-845403, EP-A-710601, EP-A-786394 and DE-A-3837981 refer to power steering systems in which the distribution core carries out a linear translation movement along its axis, relative to its fixed distribution body. Said linear movement does not exceed 3 mm, which is only sufficient for directing the oil flow towards either chamber of the actuator controlling the wheels"" rotation. This short movement of about 3 mm corresponds to a wheel""s angular rotation path of only 1xc2x0-2xc2x0.
The present invention aims at overcoming the disadvantages and drawbacks of the prior art, and at proposing an oleodynamic distribution system of the rotating type that has a particularly interesting application in the field of steering systems for rear axles of vehicles, as well as for axles in trailers and semitrailers.
More specifically, the present invention aims at proposing an oleodynamic distribution system of the rotating type that makes it possible to use an actuating cylinder normally found in commerce for the steering power control of the axle. Another important feature of said cylinder is that, in case of a steering control transmitted by a Bowden control cable, it makes it possible to avoid the employment of expansion members in order for a full angular movement of the hydraulic power steering system lever to occur even when the wheels of the rear axle are blocked in their most unfavourable position.
A further aim of the present invention is that of proposing a distribution system that contrary to any other solution known in the art is also capable of being positioned on the driven axle, in so doing obtaining a direct transmission of the steering actuation and remarkably reducing the mechanical components of the steering system.
A further aim of the present invention is that of proposing a distribution system provided with safety means that make it possible to take the driven wheels of the rear axle back to the neutral straight ahead travelling position automatically, avoiding dangerous and even life-threatening deviations of the vehicle.
A further aim of the present invention is that of proposing an oleodynamic distribution system of the rotating type that acts over a much wider rotation angle, that is anyway higher than the rotation width of the wheels to control of the axle of the vehicle, so as to be capable of controlling the steering of the wheels over their whole rotation angle.
A further aim of the present invention is that of supplying a distribution system of the rotating type that is suitable for being used for applications where the steering control signal is transmitted both mechanically and electronically or electromechanically.
This is accomplished by dint of a distribution system of the rotating type having the features given in the independent claim.
Dependent claims outline particularly advantageous forms of embodiment of the device according to the present invention.
The oleodynamic distribution system of the rotating type according to the present invention comprises a first section called xe2x80x9ccorexe2x80x9d, which is pivotal around a rotation axis and connected by a suitable mechanical member, for example a lever that is rigidly coupled with the rotation axle, to the system that supplies the control to the device itself; depending on the specific case, the core is connected to the front wheel steering system of a vehicle by dint of suitable mechanical or electronic or electromechanical means.
Said core is encased in a second section on which the conduits for forwarding the pressurised oil towards the two chambers of an actuating cylinder; according to different forms of embodiment, in the field of steering systems for rear steering axles in vehicles, or in trailers or semitrailers, the core is designed so as to allow a hydraulic drive angular rotation which is as wide as 58xc2x0, both clockwise and anticlockwise, with respect to a conventional equilibrium and starting position, corresponding with a driven wheel situation that are controlled aligned in the same direction, that is of a vehicle that is moving in a straight-ahead direction.
Therefore, the distribution system according to the present invention succeeds in having an angular clearance that is wider than the steering angle of the wheels themselves over the whole angle width within which the wheels themselves are turned.
Furthermore, said angular excursion allows the complete angular movement of the hydraulic power steering system lever, even with the rear axle wheels blocked in their most unfavourable position.
Attention is now drawn to the fact that for the purpose of the present application, by rotation of a wheel it is meant in any case the rotation of the wheel itself around an axis that is substantially vertical, said steering to obtain a change in direction of the vehicle onto which the wheel is fixed.
According to an aspect of the present invention, the driving action exerted onto the core by the angular movement of the wheels of the front axle causes the passage of pressurised oil to one of the chambers of a double effect actuator which in turn causes the rotation of the wheels of the driven axle until the second section that is connected to said wheels of the driven axle has rotated by an angle that is identical with that by which the core has been rotated.
According to the present invention, on the driving shaft a couple of sunken surfaces opposite to one another is provided. These surfaces are suitable for cooperating with a sphere onto which the end of a spring acts, said spring having its other end rigidly coupled to the second body of the distribution system.
Such an arrangement creates a centring couple of the hydraulic distribution; in fact, when the sphere is in contact with both the sunken surfaces at the same time, the core is centred with respect to the casing, with the ensuing centring of the hydraulic distribution.
During the driving action, the sphere is in contact with just one misaligned surface that activates a couple reacting to the driving, that is proportional to the spring load and to the inclination of the sunken surface, this resulting in a force that tends to automatically take the hydraulic distribution to its centred position, therefore to equilibrium, when the rotating action of the driving shaft comes to an end.
The male rotating distribution unit is hydraulically balanced on account of its constructive shape, therefore under whatever pressure the hydraulic pushes form all directions have a resulting force equalling to nought.
This implies several marked advantages from the manoeuvring point of view, this being easy and light, as well as in terms of mechanical reliability and duration of the device according to the present invention.
According to an advantageous form of embodiment of the present invention, the core is rigidly connected to its own driving shaft by a joint of the xe2x80x9cOldhamxe2x80x9d type, in a not constraining way, such a thing allowing the core to keep hydraulically balanced or in equilibrium, within the distribution system and allowing it not to be affected by possible strains coming from the outside environment.
According to a further particularly advantageous form of embodiment of the present invention, in case the application for the steering of the rear axles of the power chassis or of axles of trailers or semitrailers, the distribution system is provided with an automatic safety device which is capable of automatically taking the wheels to their equilibrium position that corresponds with the straight ahead travelling condition, in case of fault or breakdown of the steering control transmission system.
In particular, on the driving shaft of the distribution unit there is found to be located an automatic positioning member with respect to its own original position, corresponding to a straight ahead travelling position of the driven axle.
Such a positioning member comprises a spring that depending on the specific case, can be tangentially or axially strained with respect to the position of the driving shaft; when strained, such a spring exerts a force onto the core that tends to take it back to its original position.
Therefore, wherever there were found to occur a lack of electronic control or of the mechanical drive because of a breakdown or failure of the Bowden control cable, this implying a disruption of the connection between power chassis and controlled axle, said spring ends up acting automatically taking the core back to its position that corresponds with its straight ahead and centred travelling position of the wheels, in so doing avoiding dangerous changes of direction of the vehicle.